In xerographic and electrostatographic marking machines, a photoconductor P/C, generally comprising a photoconductive insulating material adhered to a conductive backing, is charged uniformly and exposed to a light image of an original document to be reproduced to form latent electrostatic images. The latent electrostatic images are then rendered visible by applying one or more pigmented resins specifically designed for this purpose; these pigmented resins are commonly referred to as toners. In the case of a reusable P/C, the toner that forms the visible images is transferred to plain paper, after which the toner images are affixed to the copy medium, usually through the application of heat and pressure, such as with a roll fuser.
One fuser is the nip forming roll fuser: a roll fuser in which a nip is formed by deforming a softer fuser roll with a biased harder roll, the softer fuser roll being heated and including, for example, an outer deformable coating of silicon rubber. The harder roll is usually not heated and is a pressure roll biased against the softer fuser roll to create the nip therebetween. Copy sheets bearing electrostatically affixed toner images pass through the nip with the images contacting the heated roll.
Roll size depends upon a number of variables, such as the copy making speed of the machine: faster machines use relatively larger rolls, whereas slower machines use smaller diameter rolls (i.e. 1 to 2 inch diameter). With the smaller rolls, copy sheets release or fall away from the nip forming fuser roll, thereby coming to rest on the pressure roll mounted beneath the fuser roll, which can result in the copy sheet taking the general shape of the pressure roll. One such fuser arrangement was found to produce between ½ to 1 inch flat curl, which bends away from the image. The copies in some cases form scrolls and can cause post fuser handling problems, particularly with regard to stacking of the copies in the output tray.
In addition to the fusing operation, as the sheet of support material passes through the various processing stations in, for example, an electrophotographic printing machine, a curl or bend is frequently induced therein. Occasionally, this curl or bend may be inherent in the sheet of support material due to the method of manufacture thereof. It has been found that this curl is variable from sheet to sheet within the stack of sheets utilized in the printing machine. The curling of the sheet of support material causes handling issues as the sheet is processed in the printing machine. Sheets delivered in a curled condition have a tendency to have their edges out of registration with the aligning mechanisms employed in the printing machine. In addition, curled sheets tend to frequently produce jams or misfeeds within the printing machine. This problem has been resolved by utilizing bars, rollers or cylinders which engage the sheet material as it passes through the printing machine. Frequently, belts or soft rollers are used in conjunction with a hard penetrating roll to remove the curl in a sheet. However, systems of this type have disadvantages. For example, the size of the de-curler is not necessarily consistent with that required in electrophotographic printing machines. In addition, decurlers of this type cannot decurl under stress conditions since they do not strain the sheets due to belt flexing.
Various approaches have been devised to improve sheet de-curlers such as described in U.S. Pat. No. 4,326,915 to Mutschler, U.S. Pat. No. 4,571,054 to Bowler, Jr., U.S. Pat. No. 4,591,259 to Kuo, et al., U.S. Pat. No. 4,627,718 to Wyer, U.S. Pat. No. 5,237,381 to Hamada, U.S. Pat. No. 5,270,778 to Wyer, U.S. Pat. No. 5,548,389 to Bowler, Jr., U.S. Pat. No. 5,848,347 to Kuo, et al. The disclosures of the foregoing patents are incorporated by reference into the disclosure of the instant patent application.
These and other prior technologies demonstrate a need for an improved decurler, especially a decurler for use in a xerographic or electrophotographic printer that is able to decurl in the direction towards the image on the sheet as well as decurling in the direction away from the image on the sheet. Previously, this has been accomplished by using two separate decurlers, one for each curl direction. In addition, instead of the need for an expensive support structure for a decurler apparatus, there exists a need for a simple and relatively inexpensive decurler apparatus. In addition to these and all the other advantages of a decurler apparatus as referred to above, it would be advantageous if the user of a xerographic or electrophotographic printer having a decurler apparatus as part of its finishing process could easily adjust the amount of decurling in the paper sheets. Accordingly, embodiments provide a new and improved decurler apparatus for use in a printing machine such as a xerographic or electrophotographic printer that will exhibit all of the specific advantages referred to above.
All of the foregoing advantages and others in accordance with the features of embodiments are attained by embodiments including first, second, third, and fourth rolls configured to form first and second nips, with the first nip comprising the first and second rolls and the second nip comprising the third and fourth rolls. Respective bearings support ends of the first and second rolls, but the third and fourth rolls are supported by the first and second rolls. In embodiments, the third and fourth rolls each have a substantially uncompressible surface, while the first and second rolls each have a compressible surface into which the third and fourth rolls selectively penetrate, respectively. A curl adjuster connected to the first and second nips controls the selective penetration of the compressible surfaces by the substantially uncompressible surfaces. A gate member in communication with the first and second nips sends sheets to one of the first and second nips for application of respective types of curl. At least one of the compressible first and second rolls comprises an elastomer as the compressible surface, and in embodiments, both the first and second rolls comprise an elastomer and outer surfaces of both the first and the second rolls are formed of the same elastomer material.
The first roll and the second roll can each be independently engaged by a respective cam, but embodiments provide for linkage of the two so that forces imposed by the curl adjuster and the rolls remain balanced. In addition, at least one bearing can be employed to support the third and fourth rolls. In embodiments, the at least one bearing supporting the third and fourth rolls is a block of low-friction material against which the third and fourth rolls bear. The at least one bearing can be, for example, a respective block of low-friction material against which the third and fourth rolls bear, or the at least one bearing can be at least one roller type bearing. If the at least one bearing is a block of low-friction material, at least a coating of fluoropolymer can be advantageous as the low-friction material.
The curl adjuster can comprise one curl adjustment device operative to adjust the amount of curl induced by the first nip and another curl adjustment device operative to adjust the amount of curl induced by the second nip. Embodiments employ a cam on a cam shaft driven by an actuator such that rotation in one direction forces one roll of a respective nip against the other roll of the respective nip. The cam can bear on a cam follower that includes a spring such that a resultant spring force is what forces the one of roll toward the other rolls. Advantageously, the curl adjuster can include respective curl adjustment devices for the first and second nips, with springs biasing one roll of each nip against the other roll of each nip. In such a dual-adjustment arrangement, each curl adjustment device can include a cam on a cam shaft driven by an actuator to adjust an amount of bias induced on the rolls by the spring, the actions of the actuators being linked to preserve force balances and/or distributions.
In other words, embodiments contemplate a quad-roll decurler including first and second nips configured to induce different curls in sheets passing therethrough. Each nip includes a compressible roll and a substantially uncompressible roll. At least one curl adjuster adjusts an amount of curl induced by at least one respective nip, and a decision gate sends sheets to one of the first and second nips in response to curl of the sheets. At least one bearing supports the uncompressible rolls, and the at least one bearing can be at least one block of low-friction material against which at least a portion of one or both of the uncompressible rolls bears. Alternatively, a plurality of blocks can support the at least one portions of the uncompressible rolls. In either case, the low-friction material can be at least a coating of a fluoropolymer, such as PTFE.
In still other words, embodiments contemplate a quad-roll decurler comprising two nips each exerting pressure on sheets passing therethrough, the pressure inducing curl in the sheets, and the decurler further comprising a curl adjustment device that adjusts the pressure exerted by at least one of the nips to adjust an amount of curl induced by the at least one of the nips. A base pressure can be induced by a spring extending between the two nips, and the curl adjustment device can counteract the base pressure of the spring to adjust the pressure. The pressure in each nip results from penetration of a substantially non-compressible pinch roll into a compressible roll, the penetration resulting from the action of at least one actuator.
As a result of the configuration of embodiments, the degree of curl induced by the first and second nips can be adjusted via the curl adjustment device. Advantageously, unlike previous decurlers, no drive reversal is required to switch from curl being applied in one direction by one of the nips to curl being applied to the opposite direction by the other nip.
Additional advantages of embodiments will be set forth in part in the description that follows, and some will be apparent from the description, or may be learned by practice of the invention in accordance with various features and combinations as particularly pointed out in the appended claims.